The invention relates to a lightweight, high-strength double wall duct system for use in jet aircraft. The system is particularly useful in jet aircraft where weight saving is important. One of the uses of the system is to carry compressed bleed air to the interior of the aircraft from jet engines in which the air has been compressed by the engine compressor and bled off from the engine forwardly of the burning chambers. The ducts may be made from thin sheet metal, such as titanium, aluminum, Inconel 625 alloy or Cres 321 alloy.
Prior ducting for the same purposes has been made from metal having a thickness of from 0.020 to 0.025 inch, which in a single tube duct has approximately the same strength as the double wall duct, according to the invention, but weighs approximately two times as much.